1. Field of the Invention
The present invention relates to an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device, and particularly to an MVA-mode liquid crystal display device having high display response speed and high quality.
2. Description of the Related Art
An MVA-mode liquid crystal display device (see, for example, Japanese Unexamined Patent Application Publication No. H11-242225, claims) is a liquid crystal display device for which the vertical alignment technology for realizing a high contrast and high response speed, and the multi-domain technology for realizing a wide viewing angle are combined.
In an MVA-mode liquid crystal display device, since part of the liquid crystal molecules are aligned with some tilting caused by previously installed protrusions or the like, it is possible to make the display response speed higher compared with conventional liquid crystal display devices. Also, since the liquid crystal molecules are aligned in plural separate orientations, a wide viewing angle of 160° towards the upside, downside, right and left directions at a contrast ratio of 10 or higher is realized.
In addition, in this technology, it is not necessary to perform a rubbing treatment, which is a major cause of decrease in the productivity, owing to a body for regulating the alignment (structures having uneven portions such as protrusions, or slit patterns in an electrode) installed on the substrates to realize the multi-domain alignment. Accordingly, a high productivity is realized.
However, even in this MVA-mode liquid crystal display device, there is a problem of not always being able to have a sufficient response characteristics. For example, when a liquid crystal is aligned with application of a voltage, the speed for propagating the tilting of alignment of the liquid crystal is relatively small in a region where there are no structures for regulating the tilting direction, and accordingly, it needs some time for the liquid crystal molecules in the whole pixel to respond.
Particularly in a lower region of the gray scale, there is a problem that the propagation of liquid crystal alignment is slower due to a lower application voltage. The response time would be three times or more of the usual value.
To solve the above-described problems, liquid crystal display devices were designed to have a constitution in which the liquid crystal molecules were aligned symmetrical to each other about the center surface between a pair of substrates, or symmetrical to each other about a certain surface perpendicular to the substrates, so that only liquid crystal molecules existing locally near the structures were aligned in the bend mode by the slopes of the structures to contribute to the display. As a result, the time required for the liquid crystal to be aligned became shorter, and the display response speed was improved (see for example, Japanese Unexamined Patent Application Publication No. 2001-235748, claims). However, MVA-mode liquid crystal display devices employing such bend alignment had a problem of unstable liquid crystal alignment. For example, when the surface of a liquid crystal panel was pressed with a finger, there appeared marks, which remained or did not disappear for a long time.
In addition, there is a strong need for further improvement of the display response speed, as television sets with liquid crystal displays are becoming popular.
The present invention is directed to solving such problems with respect to the stability of liquid crystal alignment, and to providing a liquid crystal panel and a liquid crystal display device that have stable liquid crystal alignment, excellent display quality, and high display response speed. Other objects and advantages according to the present invention will be clarified by the following explanation.